1. Field of the Invention
This invention relates to field data gathering techniques for any phenomenon where an event count per unit time can be related to the phenomenon. In particular, the invention relates to a wind prospecting instrument for remote field sites wherein raw data are preprocessed by wind run techniques. The wind run techniques are employed to develop a plurality of interrelated variables indicative of wind conditions at the site of the instrument. The invention herein will be described as it relates to wind prospecting, but other applications will be apparent by analogy.
It is desirable to provide a technique for acquisition and registration of specific information about wind movement at a wide variety of specific sites under various conditions employing the minimum amount of instrumentation. Specifically, it is desirable to retrieve sufficient information about each site or area of interest to allow satisfactory calculation of at least the wind energy density, herein notated as E.sub.0, the mean energy wind speed, v.sub.e, the mean wind energy variability, .sigma..sub.e, the mean wind speed, v, and the mean wind variability .sigma..sub.t. Meteorological conditions and terrain, particularly in mountainous areas, are so diverse that interpolation and extrapolation of conditions at regional sites, such as weather stations of the National Weather Service, are often not meaningful.
Recently Dr. Edwin X Berry of Atmospheric Research and Technology, Inc., of Sacramento, California, developed and reported on certain advanced theoretical techniques for analysis of wind energy. (See Berry, WIND RESOURCE ASSESSMENT IN CALIFORNIA, California Energy Commission Report, May 1979.) According to Dr. Berry's report, there are two key density functions useful to wind analysis, namely, the time density function, t&lt;v&gt;, which is the amount of time between any two wind speeds in time per wind speed, and the energy density function, e&lt;v&gt;, which is defined as EQU e&lt;v&gt;=1/2.rho.v.sup.3 t&lt;v&gt; (in units of energy density per wind speed),
where .rho. is air density.
These two density functions, the time density function and the energy density function, are characterized by key time-related intervals as follows:
______________________________________ T.sub.0 = .intg.dt (Time to gather sample) T.sub.1 = .intg.vdt (Wind run) T.sub.2 = .intg.v.sup.2 dt E.sub.0 = 1/2 .rho..intg.v.sup.3 dt (Total energy in the sample) E.sub.1 = 1/2 .rho..intg.v.sup.4 dt E.sub.2 = 1/2 .rho..intg.v.sup.5 dt ______________________________________
It should be noted that in the above integrals are taken over time rather than velocity and that EQU dt=t&lt;v&gt;dv.
Retrieval of data in the form of these time-related integrals can be used directly and indirectly in wind-energy assaying without the need for high resolution (and thus expensive and wasteful) raw data retrieval, such as continuous chart recorders, magnetic tape and/or telemetry systems. Moreover, these time-related integrals contain much information which would be omitted in long period time-sampled data retrieval techniques, such as a reliable measure of wind variability.
It is therefore the purpose of this invention to provide a simple, inexpensive and reliable method and apparatus for retrieving data in a preprocessed form which is sufficient to extract all information found in the time density function and the energy density function, including their respective integrals and moments, which can be used in wind assaying for such applications as identifying suitable sites and optimal design for electricity generating wind turbines.
2. Description of the Prior Art
A few instruments are available which compute some of the integrals useful for wind assaying. For example, an instrument is distributed by Natural Power Company of Waterford, Connecticut which employs non-linear analog amplifiers to compute energy. Because this instrument is analog in nature, it has the disadvantage of inaccuracies due to temperature sensitivity of the components.
Helion, Inc. of Brownsville, California now manufactures a microprocessor-based data logger system which was developed after the present invention. The Helion instrument has the capability of generating the integrals related to the energy density and the time density functions using a simple multiplier and summer. This instrument is considered complementary rather than a suggestion of the present invention, since it may be used for detailed analysis and further surveying of specific sites. The instrument has the disadvantage that it is not designed to sample and compute the integrals of interest on a substantially continual basis. Rather, it is understood that the instrument operates intermittently, collecting raw data and then processing the data in accordance with instructions in its preprogrammed microprocessor. As a further disadvantage, it does not have a field readout feature. Its usefulness is generally limited to applications where power is readily available or the instrument is frequently monitored, or to applications where intermittent sampling of conditions will suffice. It is understood that the Helion instrument does not preprocess retrieved data to the extent herein taught.